Additive synthesis of sound involves the electronic creation of complex waveforms by adding together simple waveforms such as sine waves. The simple waveforms are "partials" or "harmonics" of the resulting complex waveform. The electronic waveform, which may be represented digitally, or as a voltage, or by other electronic means, is converted to audible sound by known means including D/A conversion and an amplifier-loudspeaker combination.
This method has been applied to commercially available sound synthesizers. Examples include the Kawai Model K5, and recently the Kawai Model K5000. (See, http://www.ozemail.com.au/.about.kawaioz/k5000.htm). These synthesizers allow the user to independently specify the amplitude of up to 128 harmonics. As the number of harmonics increases, additive synthesis becomes a more powerful method, capable of generating more complex sounds. However, it also becomes more unwieldy to use due to the number of parameters that must be specified by the user.
Editing softward for the Kawai K5000 is available from Emagic Soft- and Hardward GmbH, however, it does not enable functional specification of harmonic profiles. (See, http://www.emagicusa.com/english/products/index.html).